1. Technical Field
The invention relates generally to field emission electron sources and, particularly, to a carbon nanotube field emission electron source employing a getter to exhaust unwanted gas from therein, thereby ensuring a high degree of vacuum. The invention also relates to a method for making a field emission electron source.
2. Discussion of Related Art
Carbon nanotubes (also herein referred to as CNTs) are very small tube-shaped structures, each of which is essentially a graphite sheet in a tubular form. Carbon nanotubes have interesting and potentially useful electrical and mechanical properties and offer potential for various uses in electronic devices. Carbon nanotubes also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e., length/diameter ratios) (e.g., potentially greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features tend to make carbon nanotubes ideal candidates for field emission electron sources.
Generally, a CNT field emission electron source includes a conductive base and at least one carbon nanotube formed on the conductive base. The carbon nanotube acts as an emitter of the field emission electron source. The methods adopted for forming the carbon nanotube on the conductive base mainly include mechanical methods and in-situ synthesis methods. One mechanical method is performed by placing a synthesized carbon nanotube on a conductive base using an Atomic force microscope (AFM) and then fixing the carbon nanotube on the conductive base via a conductive paste or other adhesives. The mechanical method is relatively easy to carry out. However, the precision and efficiency thereof are relatively low. Furthermore, the electrical connection between the conductive base and the carbon nanotube tends to be poor because of the limitations of the conductive paste used therebetween. Thus, the field emission characteristics of carbon nanotubes mounted in this manner are generally unsatisfactory.
One in-situ synthesis method is performed by coating metal catalysts on a conductive base and synthesizing a carbon nanotube directly on the conductive base by means of chemical vapor deposition (CVD). The in-situ synthesis method is relatively easily performed. Furthermore, the electrical connection between the conductive base and the carbon nanotube is typically good because of the direct engagement therebetween. However, the mechanical connection between the carbon nanotube and the conductive base often is relatively weak and thus tends to be unreliable. Thus, in use, such a carbon nanotube is apt, after a period of time, to break away from the conductive base due to the stress of the electric field force. Such breakage would damage the field emission electron source and/or decrease its performance. Furthermore, in the in-situ synthesis method, controlling of the growth direction of the carbon nanotube is difficult to achieve during the synthesis process. Thus, the production efficiency thereof is relatively low, and the controllability thereof is less than desired. Still furthermore, the in-situ synthesis method has a relatively high cost.
Additionally, in order for the field emission electron source to successfully emit electrons, a vacuum condition must be provided for the field emission electron source. Accordingly, a getter device is arranged beside/proximate the field emission electron source to exhaust the unwanted gas therearound to thereby ensure a high degree of vacuum to promote effective electron emission. This arrangement is a disadvantage as it increases the fabrication cost of the field emission electron source.
What is needed, therefore, is a field emission electron source that overcomes the above-mentioned shortcomings. The field emission electron source should, beneficially, have a better electrical connection and mechanical connection between a conductive base and a CNT thereof. Also, a high degree of vacuum, gained for a low fabrication cost, is desired for the field emission electron source, in order to ensure, in an economical manner, a better and more steady field emission performance during the use thereof.
What is also needed is a method for making such a field emission electron source.